a) Field of the Invention
The present invention relates to a method of manufacturing a semiconductor device including a step of forming a fine pattern on a highly reflective substrate by using an anti-reflection film which prevents light beams for exposing a photoresist film from being reflected at the substrate surface.
b) Description of the Related Art
If light beams for exposing a photoresist are strongly reflected at the surface of a substrate, the region of the photoresist not intended to be exposed may sometimes be exposed. If such reflection cannot be suppressed, the resist pattern after the development may be partially thinned. In order to form a fine pattern at a high precision, it is necessary to suppress reflected light at the substrate surface.
Lithography technique of forming an anti-reflection film under a photoresist film has been investigated. Substance which absorbs light having the wavelength in the range of exposing light is generally selected as the material of an anti-reflective film.
An amorphous carbon (a-C) film can be used as an anti-reflective film of exposing light, from the standpoint of its optical property. An a-C film is a film having carbons without long range ordering as its main composition, including those having the structure almost like a carbon crystal structure and those like organic substances. An a-C:H film is an amorphous carbon film whose dangling bonds are terminated with hydrogen atoms. Amorphous carbon unless otherwise specified also includes the substance made of only carbons without any hydrogen atom. Generally, a-C film is simply called a carbon film in some cases.
Japanese Patent Laid-open Publication No.60-235426 discloses a method of depositing a carbon film on the surface of an Al film to a thickness of 100 nm as an anti-reflection film to be used when a photoresist film on the Al film is exposed. It teaches that a deposited carbon film can subdue a warped or constricted pattern.
An a-C film is absorptive relative to ultraviolet light. A complex index of refraction of an a-C film has a real part and an imaginary part. An a-C film formed on an Al film provides ordinary anti-reflection effect by interference and also operates to attenuate light amount incident to the Al film surface by absorption.
However, it is not certain what kind of a carbon film ensures the anti-reflection effects during a photolithography process. The technology of etching a carbon film used as an anti-reflection film becomes important. However, the etching technology ensuring a process precision sufficient for semiconductor manufacturing processes has not been established as yet.
If a desired resist pattern cannot be formed after a resist film coated on a carbon film is exposed and developed, another resist film is re-made. If both the anti-reflection carbon film and the resist film thereon are to be removed, the processes become complicated. The technique of removing only the resist film without damaging the anti-reflection effect of the underlying carbon film has not yet been established.
The anti-reflection effect of a carbon film deposited on a substrate are not sufficient if a fine pattern, particularly, a pattern of 1 xcexcm or less, is to be formed on a highly reflective substrate. The main reason for this is considered to lie in the reflection of exposing light transmitted through the anti-reflective film, at the surface of the highly reflective substrate. Another reason is considered to lie in the influence of exposing light reflected at the surface of the anti-reflective film because the reflection at the anti-reflective film surface cannot be eliminated.
Therefore, upon patterning a resist film formed on a substrate having a step portion, the line width of the pattern may sometimes change in conformity with the shape of an underlying film because of halation or the like.
The binding energy of carbon is very high so that conventional techniques provide a slow etching rate of the carbon film and a low etching selection ratio between a resist film and the carbon film. It is therefore necessary to thicken a resist film when a carbon film is used as an anti-reflective film, which lowers an exposure precision at the worst.
It is also difficult to remove a carbon film completely. For example, if a carbon film cannot be removed completely and is left between a W wiring layer and an interlevel insulating film, adhesion strengths between the wiring layer and carbon film and between the carbon film and interlevel insulating film are poor. If there is a left carbon film, good electrical connection at a contact hole is not ensured.
An object of the present invention is to provide an exposure technique allowing formation of a fine pattern on a highly reflective substrate with less variation of pattern sizes and at high precision.
Another object of the present invention is to provide a technique of etching a carbon film at a high etching selection ratio relative to a resist film and a technique of removing a carbon film.
Further object of the present invention is to provide a technique of completely removing a resist film without giving substantially influencing an under lying carbon film. According to one aspect of the present invention, there is provided a method of manufacturing a semiconductor device including the steps of: forming a transparent film on a light reflecting surface, the transparent film having an absolute value 0.2 or smaller of an imaginary part of a complex refractive index; forming an anti-reflective film on a surface of the transparent film, the anti-reflective film having an absolute value 0.3 or larger of an imaginary part of a complex refractive index; and coating a photoresist film on a surface of the anti-reflection film and patterning the photoresist film by applying light to a necessary area of the photoresist film, wherein the thicknesses of the anti-reflective film and the transparent film are so selected as to set a standing wave intensity Isw=Ixcex4/Iave to 0.2 or smaller, where Iave is an average value of light intensity in the photoresist film, the standing wave being generated by a superposition of light incident to the photoresist film and light reflected from the anti-reflection film, the transparent film, and the light reflecting surface, and Ixcex4 is an amplitude of a light intensity change.
According to another aspect of the present invention, there is provided a method of manufacturing a semiconductor device including the steps of: preparing a substrate having an exposed amorphous carbon film on at least part of a surface of the substrate; and removing the amorphous carbon film by dry etching at a substrate temperature of 70 to 450xc2x0 C. by using at least one of gases selected from the group consisting of reducing fluoride gas, halogen gas, and gas containing oxygen.
A transparent film and an anti-reflection film laminated in this order on a light reflective surface are selected to have proper film thicknesses. With the proper film thicknesses, it is possible to reduce the total amount of light reflected from the light reflective surface, transparent film surface, and anti-reflection film surface. It becomes therefore possible to reduce the component of a standing wave generated by a superposition of light incident to a resist film formed on the surface of the anti-reflection film and light reflected from all the light reflective surfaces.
With the reduced component of a standing wave, halation can be eliminated and a fine pattern can be formed at a high precision.
An amorphous carbon film can be efficiently etched at a substrate temperature of 70 to 450xc2x0 C. by using reducing fluoride gas, halogen gas, or gas containing oxygen.
As described above, use of a laminate structure of an anti-reflection film and a transparent film respectively having a proper film thickness allows a resist pattern to be formed on a highly-reflective surface at a high precision. Even if an amorphous carbon film is used as an anti-reflection film, it can be selectively and completely removed at a high precision. Accordingly, a lead wire via a contact hole can be connected with good yield.